Plasticization, Cross-linking And Compounding Of Wheat Gliadin Films

In recent years,the development and application of petroleum-based polymers not only aggravated the consumption of world oil resources,resulted in the decrease of resources,but also caused serious impact on the ecosystem and the living environment.The limitation and unsustainability of petroleum resources make it urgent to develop alternative natural polymer materials.At present,the research,development and industrialization of environment-friendly materials have become important issues.Wheat gliadin is the main component of wheat gluten.Because of its unique viscoelasticity,good degradability and reproducibility,gliadin has become a new material with great potential for development.In this paper,different types of gliadin films were prepared by thermo-compression molded method with gliadin as the main raw material,glycerol and polyethylene glycol as plasticizer,ε-polylysine as crosslinker with TG enzyme and microcrystalline cellulose as reinforcement.The effects of different conditions of molding-compression,plasticizer and modifier on the structure,surface morphology,mechanical properties,light transmittance,hygroscopicity and water stability of the gliadin films were studied.Using glycerol and polyethylene glycol(PEG200)as plasticizer,gliadin films were prepared by thermo-compression molded method.It was found that when glycerol was used as plasticizer,gliadin flims with the best mechanical properties could be obtained by thermo-compression molding at 140℃ for 12 min.The breaking strength of the film was 5.27 MPa,the elongation at break was 109.4%,the swelling degree was 102.86%,the solubility was 16.63%.When PEG200 is used as the plasticizer,gliadin flims with the best overall properties could be obtained by thermo-compression molding at 154℃ for 3 min with PEG200 content was 15%.The breaking strength of the film was 18.38 MPa,elongation at break was 5.95%,swelling degree was 103.99%,solubility was 15.52%.Compared with the glycerol plasticized gliadin films,the breaking strength of the PEG200 plasticized films was about 3.487 times,but the elongation at break was only 5.4%,while the water stability was worse and the hygroscopic rate was higher.Therefore,glycerol plasticized gliadin film has better overall properties.Crosslinked gliadin was prepared by TG enzymatic crosslinking of ε-polylysine and gliadin,and crosslinked gliadin films were prepared by thermo-compression molded method.It was found that when the content of ε-polylysine was 4%,the overall properties of gliadin films were the best.The breaking strength of the film was 6.02 MPa,the elongation at break was 135.24%,the moisture absorption rate was 9.64%,the antibacterial rate of Escherichia coli was 97.8%,the antibacterial rate to Staphylococcus aureus was 88.8%,and the Klebsiella pneumoniae rate was 97.7%.Compared with the non-crosslinked gliadin,the molecular weight of crosslinkedgliadin increased significantly,the thermal stability was better,and the crystallinity increased slightly.Composite protein films were prepared by thermo-compression molded method with aldehyde based microcrystalline cellulose(AMCC)as filler and gliadin as substrate.It was found that the aldehyde group introduced after modification of microcrystalline cellulose has double effects on the gliadin film.The breaking strength of the AMCC/ crosslinked gliadin film was 17.54 MPa,the elongation at break was 12.49%,the modulus of elasticity was 4.88 GPa,the hardness was 316.47 MPa,the hygroscopic rate was 7.44%,the swelling degree was 74.82%,the solubility was 16.16%.Compared with the gliadin film,the breaking strength of the AMCC/ crosslinked gliadin film increased by 48.09%,the moisture absorption rate decreased by 4.35%,the swelling degree decreased by 19.30%,and the solubility decreased by 20.23%.After compounding AMCC with crosslinked gliadin,the mechanical properties and water stability of the films increased significantly.